Francis napier denison



(No Model.)

F. N. DENISON. SHORT OIROUITING DEVICE FOR STOPPING DENTAL MOTORS.

No. 543,855. Patented Aug.6,1895.

UNITED STATES PATENT OFFICE.

FRANCIS NAPIER DENISON, OF TORONTO, CANADA.

SHORT-CIRCUITING DEVICE FOR STOPPING DENTAL MOTORS.

SPECIFICATION forming part of Letters Patent No. 543,855, dated August6, 1895.

7 Application filed October 9, 1894. Serial No. 625,326. (No model.)

To aZZ whom it may concern:

Be it known that I, FRANCIS NAPIER DENI- SON, of the city of Toronto, inthe county of York, in the Province of Ontario, Canada, have inventedcertain new and useful Improvements in short Oircuiting Devices forStopping Dental Motors, of which the following is a specification.

My invention relates to a short-circuiting device for the instantaneousstoppage of an electric motor more particularly adapted for running adental engine, and referring particularly to a former application ofmine for improvements in dental-motor outfits, filed on the 26th day ofMay, 1894., under Serial No. 512,537, in which a peculiar construction 0foot-switch is used.

The object of the invention is to provide means for short-circuiting thearmature of the motor no matter at what rate of. speed the motorarmature-shaft may be rotating, so as to thereby stop the shaftinstantaneously without the necessity of employing any means to decreasethe speed of rotation of the armature; and it consists essentially oftwo contact-plates, preferably arc-shaped in form, insulated from thebase-plate of the switch and each connected to the armature of themotor, but separated from each other, and a spring contact-plateconnected to the bottom of the toe-plug of the pedal of the foot-switch,which plug is of insulating material, this contactplate being arranged,when the heel of the pedal of the foot-switch is depressed, to bridgethe contact-plates and thus short-circuit the armature no matter intowhat position the toe may be swung for the purpose of speeding the shaftof the motor, the foot-switch being otherwise constructed as describedin my former application above referred to, with the exception thatthere is no provision made for operating the brake therein provided,which brake, by my present device, is entirely dispensed with.

Figure 1 represents a view, partially in perspective and partiallydiagrammatic, showing the footswitch, wiring, motor, hand-switch,shunt-field, and connections, the foot-switch being shown in an enlargedperspective view, a portion of the plate or frame of the switch beingbroken away. Fig. 2 is a plan View of the rheostat inverted.

For the purpose of clearly illustrating my invention I shall firstdescribe the major portion of the foot-switch in detail, as in my formerapplioatiomand in so doing will point out the difference in constructionnecessary to accomplish the present object I have in view.

U is the base plate of the foot-switch, which is made hollow, asshown,andV is the pedal, which is stiffly pivoted, swiveled, andarranged as described in my former application.

U U are hollow stop-pins attached to or forming part of the base-plateU.

W is a bar of insulating material secured to the bottom of thebase-plateU. A great deal of the bar W is broken away, so as to exhibit details ofconstruction.

X is a bar of insulating material pivoted at the center by the screw-pinm to the bar V.

0a m are pins which are secured on the ends of the bar X. The pins as 00extend rearwardly into the slots m 00 formed at the bottom of theplungers X X The plungers X X are preferably provided with convexpushing-caps 00 as".

V is a downwardly-extending plug of insulating material secured to theforward end of, the pedal. The plug V is surrounded at the top by a ringV of insulating material, which is designed to limit the downwardmovement of the plug.

0 is a boss formed underneath the heel portion of the pedal V. The boss0 is provided with a rubber cushion V which is designed to limit thedownward movement of the heel portion of the pedal.

Y Y are contact-plates, preferably areshaped, which are secured to thebottom of the base-plate U and are insulated from it and eachother bythe plate Y.

V is a spring contact-plate secured on thereduced lower end of the plugV by a nut 11 of insulating material. V is a spring contact-platerigidly secured at the bottom of the insulating-plug V by the screw o Itwill be seen that the plates V and V are insulated from one another.

The spring-plate V is normally held in contact with the plates Y Y whenthe motor is at rest, and the plate V is held out of contact with one ofthe plates Z of the fiat rheostat Z, which is situated beneath thebase-plate U,

except when the foot-switch is pressed at the toe to throwin the motor.The plates Z are separated from each other and are insulated from therheostat by the plate Z".

Z are the bindingposts of the rheostat, which extend through theinsulating-plate into the rheostat. There is one bindingpost for eachplate, and the posts are connected to the plates by the wires 2 'w w arecontact-blocks secured at one end of the bar l/V, and 10 10 to are barsflush with the inner side of the bar.

X X are contact-plates secured to the front side of the pivoted bar X.The plates X K have at one end the spring ends X, which are continuouslyheld in contact with the contact-blocks w w secured to the bar NV, andat the other spring ends X X, which are designed to be respectivelybrought in contact with the bars 10 10 or w 10 this depending upon whichof the plungers X or X is pressed down. The rheostat above mentioned, inthis instance, as indicated in Fig. 2, has the greatest amount ofresistance at the right-hand side, and the resistance decreases fromright to left, the left-hand binding-post having no resistance at all.

The left-hand binding-post Z is connected by the wire 2 to thecontact-bar w". The bar 10 is connected to the bar to by the wire 2 \V\V \V are binding-posts of the 1notor and switchboard circuits which aresecured in the bottom of the bar WV.

2 2 are wires connecting the contact-plate Y with the binding-post \Vand W 3 is a wire connecting the wire 2 and contact-plate w with thebinding-post W.

4 is a wire connecting the contact-block to with the binding-post WV.

5 is a Wire connecting the contact-block to with the binding-post W 6 isa wire connected at one end to the screw and consequently to thecontact-plate V and extending up through the insulating-pin V,underneath the pedal, through the opening 11 down through the hollow pinV, as indicated by dotted lines, forward to the bindingpost WV? 7 is thepositive wire through which the curreutpasses ordinarily when thefoot-switch is not thrown in, through the wire 9, shunt-lield 10, wire11, and back by the negative wire 12.

\Vhen the forward end of the pedal of the switch is pressed down thecircuit is completed and passes through the positive wire 7 into thebinding-post V thence by the wire (3 to and through the insulating-plugv, contactplate V one of the plates .2 of the rheostat, through therheostat finally on the Wire to the binding-post Z at the left-hand sideof the rheostat, the wire ,2" to the contact-bar w, thence by thecontact-plate X to the contactblock to, thence by the wire 4 to thebindingpost XV, thence by the wire 13 to the motor, through the motor,and by the Wire 1 1 back to the binding-post W from the binding-post Wby the wire 5, to the contact-block w,

thence by the contact-plate X to the contactbar to, thence by the wire 3to the bindingpost W, thence by the wire 12 back to, through, and to theswitchboard J. The course above described is that shown when the plungerX is pressed down and the bar X in the position shown.

It will of course be understood that the direction of rotation ofarmatureshaft will be reversed, as in my former application, and thatthe nearer the pedal is swung to the left- ,hand side of the figure, soas to bring the contact-plate V upon the plates nearer the left-handside, the less the resistance will he (see Fig. 2) and consequently thegreater the speed of the motor.

It will now be seen that in order to produce a short circuit through thearmature ot' the motor and stop the rotation of the armatureshaft, theheel of the pedal V may be pressed down so as to bring the contact-plateV upwardly out of contact with the plates Z, thereby throwing thecurrent entirely out of the foot-switch. The spring contact-plate Vhoweveryis brought against the contact-plates Y Y, so as to bridge them,and an induced current will be produced in the armature shortcircuitthrough the wires l i, binding-post W wire 2, plate Y, contact-plate Vplate Y, wire 2, binding-post \V, and wire 13. It will thus be seen thatthe motor will be really acting as a dynamo for the time being and thatan instant stoppage of the armatureshaft will be effected.

By means of the short-circuiting device above described the instantstoppage of armature-shaft can be eileeted in the same time at thehighest speed as well as at the slowest speed. In my device it will alsobe seen that owing to the slow speed of armature when running at itsmaximum the short-circuiting of armature can be effected with thefully-mag netized field, as the induced current in the armature has nottime to rise to dangerouspio portions on account of the armature comingto rest instantaneously.

That I claim as my invention is 1. The combination with a motor having ashunt field and circuit completed through a foot switch as specified andthe foot switch pedal pivoted and swiveled as specified and having aplug of insulating material extending downwardly from the toe portionthrough which runs the main circuit wire to the spring contact platedesigned to be movable upon the plates of a resistance coil, so as tovary the amount of current through the main circuit and consequently therate of speed of the 1uotor, of two arc-shaped contact plates insulatedfrom each other and each connected to the poles of the armature and aspring contact plate secured near the bottom of the toe plug of thepedal, insulated from the spring contact plate movable upon the platesof the resistance coil, and so arranged that when the heel of the pedalis pressed down such contact spring will be brought into sliding contactwith the arc-shaped plates so as to bridge them as and for the purposespecified.

2. In combination with the motor havinga shunt field and a circuit, afoot switch interposed in said circuit and comprising a hollow baseplate having a rheostat beneath the same, the series of contactsconnecting therewith, the are shaped contact plates connected with thepoles of the armature, and the foot lever 10 pivoted to swing bothvertically and laterally,

and having a contact arm for engaging the said series of contacts as thepedal is swung laterally, and a second contact arm for connecting thetwo arc shaped plates as the pedal is swung vertically, substantially asde- 15 scribed.

FRANCIS NAPIER DENISON.

Witnesses:

B. BOYD, II. H. YOUNG.

